The present invention relates generally to manufacture of IC (integrated circuit) packages, and more particularly, to an apparatus and method for automatically detecting unacceptable warpage of trays for holding IC packages to prevent occurrence of bent leads on the IC packages.
Referring to FIG. 1, during manufacture of IC (integrated circuit) packages, the IC packages are placed into a tray 100 for transporting the IC packages. The tray 100 includes a plurality of pockets including a first pocket 102, a second pocket 104, a third pocket 106, a fourth pocket 108, a fifth pocket 110, and a sixth pocket 112 with each pocket holding a respective IC package. For example, an IC package 120 is placed in the second pocket 104. A tray typically has more numerous pockets, but six pockets are shown in FIG. 1 for clarity of illustration.
During manufacture of IC packages, the tray 100 holding the plurality of IC packages is heated to temperatures above 100xc2x0 Celsius for example. The tray 100 holding the plurality of IC packages after being heated is also cooled down to room temperature. With repeated heating and cooling of the tray 100 during manufacture of a high number of IC packages, the tray 100 becomes warped in shape. When the tray 100 is warped in shape, an IC package may no longer fit with the dimensions of a pocket of such a warped tray. In that case, when an operator attempts to place an IC package into or out of the pocket of a warped tray, the leads of the IC package may become undesirably bent since the IC package does not fit within such a pocket.
Thus, a tray that is unacceptably warped after repeated heating and cooling of the tray is scrapped. Referring to FIG. 2, for determining whether a tray is unacceptably warped in the prior art, the tray 100 is set on a flat table surface 130. An operator manually holds a feeler gauge 132 and slides the feeler gauge 132 under a plurality of predetermined locations of the tray 100 while the tray 100 is set on the table surface 130. Multiple feeler gauges of various thicknesses are used in this manual process. The operator starts with the thinnest feeler gauge that slides under at least one of the plurality of predetermined locations of the tray 100.
The operator then uses feeler gauges having higher thickness until a feeler gauge of limiting thickness no longer slides under any of the plurality of predetermined locations of the tray 100. The thickness of such a feeler gauge of limiting thickness determines the amount of warpage of the tray 100. A higher thickness of such a feeler gauge of limiting thickness indicates a higher amount of warpage, and a lower thickness of such a feeler gauge of limiting thickness indicates a lower amount of warpage.
Such manual determination of the amount of warpage in the prior art is time consuming as the operator works through feeler gauges of increasing thickness. In addition, the accuracy of such manual determination of the amount of warpage in the prior art depends on the skill of the operator, and such manual determination of the amount of warpage in the prior art is prone to human error. If a good tray is determined to be unacceptably warped by human error, then a good tray may be wasted in being scrapped. On the other hand, if an unacceptably warped tray is determined to be a good tray by human error, then the IC packages may not fit within the pockets of such a tray resulting in bent leads of the IC packages.
Thus, a mechanism is desired for automatically detecting unacceptably warped trays.
Accordingly, in a general aspect of the present invention, a conveyor is used for moving a tray through a laser beam such that the portion of the laser beam that is not blocked by the tray determines the amount of warpage of the tray.
An apparatus and method of one aspect of the present invention automatically detects unacceptable warpage of a tray for holding a plurality of integrated circuit packages. A conveyor holds and moves the tray along a predetermined linear path, and the predetermined linear path is along a length of the tray. Each of a plurality of tray position sensors is disposed at a respective location along the predetermined linear path, and each tray position sensor detects when an object that moves with the conveyor has reached the respective location along the predetermined linear path.
In addition, a laser beam source is disposed on a first side of the predetermined path for generating a laser beam toward a first side of the tray, and the laser beam has a field that extends through any possible height of the tray. A laser beam sensor is disposed on a second side of the predetermined path and faces toward a second side of the tray that is opposite the first side of the tray such that the laser beam sensor detects a portion of the laser beam that is not blocked by the tray.
Furthermore, a data processor is coupled to the conveyor, the plurality of tray position sensors, and the laser beam sensor. The data processor controls the conveyor to move the tray along the predetermined path. When the object that moves with the conveyor reaches a tray position sensor, the data processor controls the conveyor to stop movement of the tray such that a measured height of the tray at a measured location of the tray is determined from the portion of the laser beam that is not blocked by the tray at the measured location of the tray as detected by the laser beam sensor. The tray is determined to be unacceptably warped when the measured height is greater than a predetermined value.
The present invention may be used to particular advantage when the plurality of tray position sensors are positioned along the predetermined path such that a respective measured height of the tray is determined at each of a front location of the tray substantially toward the front end of the tray along the length of the tray, a center location of the tray substantially toward a center along the length of the tray, and a back location of the tray substantially toward a back end of the tray along the length of the tray. In that case, the tray is determined to be unacceptably warped when any of the respective measured height of the tray at the front location, the center location, or the back location is greater than the predetermined value.
An alarm unit, coupled to the data processor, warns an operator when the tray is determined to be unacceptably warped. A first counter counts a first number of unacceptably warped trays, and a second counter counts a second number of good trays that are not unacceptably warped.
In this manner, an operator simply sets and clamps a tray to the conveyor, and the tray is moved by the conveyor through a laser beam for automatically determining whether the tray is unacceptably warped. The automated mechanism for detecting trays that are unacceptably warped is less time consuming, more accurate, and less prone to human error.
These and other features and advantages of the present invention will be better understood by considering the following detailed description of the invention which is presented with the attached drawings.